This invention relates to an apparatus for the continuous molding of structural profile or section members made from hardened synthetic resins. The members are reinforced with fibrous material embedded within the profile member during the molding process. The profile member is shaped as desired by drawing through a shaped molding duct while hardening takes place under heat.
In the past, numerous problems and disadvantages have been encountered in molding processes such as this. In horizontal working methods, it has been near impossible to produce section or profile members and especially hollow profile members with a complicated cross-section. In addition, it has been difficult to introduce in a satisfactory manner fiber lengths and fabric or mat strips running from an impregnation bath and guided by a centrally arranged mandrel. Even with complicated open profile members, considerable difficulties have been experienced in the feeding of the impregnated fiber lengths and webs so that a uniform distribution of the reinforcing material is present in the profile cross-section.
In the prior art it is also known to supply resin under pressure to the fiber material for the purpose of wetting. However, in the past this wetting operation has taken place before the material has reached the shaping section of the mold. Thus, the fiber material has a dimension which is usually greater than the overall cross-section of the profile member to be produced. This impregnation at the entrance to the mold does not readily lend itself or guarantee that the fiber material will flow through the mold with the required distribution over the entire cross-section.
It is true that when using the continuous mold in the vertical position, some of these difficulties are reduced by the fact that the impregnating bath lies immediately above the mold inlet and the reinforcing material can be draped into the mold in their relative positions. A squeezing action or flowing movement, however, remains as the fibers enter the throat of the mold with a partially uncontrollable change in the fiber arrangement due to a back pressure generated by excess resin contained on the fiber material. In addition, it has been found that a heat transfer due to the chemical exothermic process in the resin is conducted upwardly into the impregnating bath causing possible premature gelling and hardening.
In the prior art molding processes, considerable sliding friction has been experienced between the walls of the shaped molding duct and the continuous length of profile member as the resin becomes hard. For this reason, the operating speed of the molding process and the length of the molding duct are limited since the withdrawal forces cannot exceed tthe reinforced material strength of the finished profile member. A cooling means placed at the inlet of the mold has been attempted to limit the excess temperatures that can be expected in the resin. This cooling section, however, reduces the length of the mold duct available for hardening of the laminate. Attempts to compensate for these effects by the use of highly reactive resins or large additions of reactive media to the resin has been found to be prohibitive. By attempting to reduce the hardening time for the resin, spontaneous hardening can result producing a brittle product or one which experiences the formation of cracks because of shrinkage stresses occurring in the mold.
Another process for the continuous molding of fiber reinforced profiles is known wherein the fibers are fed horizontally from a feeding device and are passed through a preliminary cooling zone whereafter there occurs in injection of liquid synthetic resin in order to obtain a pre-impregnation of the reinforcing material. In further advance through the molding duct, a second resin injection is performed to fit the profile member with an additional synthetic resin envelope.
In the past, other problems have existed when an attempt has been made to introduce reinforcing windings or coils into the molded profile member. Pre-impregnation of the coil fibers either prior to or at the entrance to the molding duct causes a change in the shape of the winding or coil structure. In addition, this process has produced shifting in the relative position of the coil with respect to the cross-section of the member. Furthermore, the use of woven fabrics and mat strips for this purpose has been found to be undesirable because of the necessity of butting or overlapping these materials in the reinforcing arrangements. These procedures increase the danger of irregular fiber concentrations in the finished product. Where the diameters of the longitudinal openings are intended to be small, the use of resin-impregnated mats or fabrics in the conventional process is impossible.